This invention pertains to ultraviolet curable coatings compositions. More particularly, this invention pertains to processes for rendering normally-inert polymers curable by the use of ultraviolet radiation.
The use of ultraviolet curable coating compositions has steadily increased in recent years due to desires for conservation of energy and for reduction of polluting effluents. Ultraviolet curable coating compositions are useful in both these areas, because they (1) require little energy for curing, and (2) do not in most cases produce pollutants when cured.
Heretofore, however, most ultraviolet curable compositions have been based upon essentially monomeric materials. The incorporation of acrylate unsaturation onto polymeric backbones by direct esterification between, for example, acrylic acid and an hydroxy-containing polymer, has been difficult due to the extremely high reaction temperature required to effect the direct esterification reaction. Furthermore, direct esterification reactions using either no catalyst or traditional esterification catalysts, have required extended periods of time for complete esterification. Both high reaction temperatures and extended esterification times have contributed greatly to low product yield, due in large part to polymerization which occurs during these high temperature, long-term direct esterification processes.
One method of reducing the reaction temperature is by the use of an azeotroping solvent. Most common solvents for such use include benzene, which is too toxic, and toluene and xylene, both of which have reflux temperatures which are higher than is desirable. Furthermore, benzene, toluene, and xylene exhibit in most cases total solubility with a finished product and thus require vacumn to obtain essentially solvent-free compositions.
Thus, it is an object of this invention to prepare polymeric materials which have pendant groups, such as acrylate groups, which are subject to ultraviolet curing.
It is another object of this invention to prepare highly acrylated polymeric coatings.
It is a further object of this invention to prepare acrylated coating compositions by a process utilizing an azeotroping solvent which allows reaction at significantly reduced temperatures and which solvent is easily removable after the reaction is completed.
These and other objectives are obtained by carrying out the instant invention.